1. Field of the Invention
This invention relates to rotary tabletting presses with die tables, having generally planar upper surfaces, rotatable about an axis. A press of this type is disclosed in U.S. Pat. No. 3,545,007.
2. Description of the Prior Art
Heretofore rotary tabletting presses have used conduits, fixedly extending from an elevated powder storage hopper, to transfer tabletting powder from the hopper to the preferably horizontal upper surface of a rotatable die table located below the hopper. Means for stopping powder flow consisted of a single moveable plate, resident in a groove and slidable into the conduit to block powder flow.
These sliding plates inherently possess a substantial disadvantage: when the plate slides from the open position to a closed position at which powder flow is blocked, some powder is inevitably caught and compressed between the plate and the groove. Repeated movement of the plate between open and closed positions results in more powder being caught and compressed between the plate and the groove, with consequent buildup of compressed powder. Indeed, certain materials can render the slidable plate inoperative due to material buildup in the groove. Eventually the compressed powder breaks loose, falling through the conduit and into a die cavity in the die table, where the compressed powder, along with uncompressed free-flowing powder, is pressed into a tablet. The tablet, made at least partially from already compressed powder, contains a greater mass of powder than tablets formed entirely of uncompressed powder and hence may be outside specification limits for the tablets being produced.
In the presses known heretofore, when it is desired to change the gap between the powder feed conduit discharge end and the die table, the entire powder feed hopper must be moved, since the powder feed conduit is fixed thereto. This is quite cumbersome. Additionally, when it is desired to change tools in conventional machines, the entire hopper must be removed in order to move the powder feed conduit away from the die table to provide workers with access to the die table. Again, this is cumbersome.
In tabletting presses it is desirable to be able to perform regular machine cleaning, maintenance, and tool set removal and replacement without disturbing the powder supply and without altering the powder's physical properties. It is also desirable to be able to quickly adjust powder flow without disturbing the powder supply contained in the hopper, to regulate powder head and powder flow within a powder feed frame on the press die table. Tabletting presses known heretofore, with powder flow conduits fixed relative to the storage hopper, do not conveniently provide such capabilities.